Facile wick-and-oil flame synthesis of high-quality hydrophilic onion like carbon nanoparticles

Because of their unique 0-D structure, small (<10 nm) diameter, high electrical conductivity and relatively easy dispersion, compared to 1-D nanotubes and 2-D graphene, onion-like carbon (OLC) has been shown to be ideal as an active material for supercapacitor electrodes. However, its implementation is fraught with lack of convenient methods for their high yield preparation and purification. Here we report a facile scalable and one-step "wick-and-oil" flame synthesis of OLC nanopowder from 'clarified butter' without contaminated by any other forms of carbon; thus eliminating the post processing purification procedure. Brunauer-Emmett-Teller (BET) specific surface area of as-prepared OLC was 218 m(2)/g, which is higher as compared to other reported flame synthesis methods. The as-obtained OLC powder is highly dispersible and the suspension is stable for months indicating the presence of surface functional groups which is confirmed by Fourier transform infrared spectroscopy (FTIR). It is demonstrated that by suitable choice of a precursor material, very pure and hydrophilic OLCs can be prepared in bulk quantities by flame synthesis method. An effective and simple strategy was developed to prepare flexible, binder-free OLC electrodes on cotton fabrics and demonstrated their application in a flexible supercapacitor device. The capacitance of OLC is 102 F/g with a measured power density of 1224 W/kg and an energy density of 3.5 W h/kg in 1 M Na2SO4 as the electrolyte. (C) 2016 Elsevier B.V. All rights reserved

Designing binder-free, flexible electrodes for high-performance supercapacitors based on pristine carbon nano-onions and their composite with CuO nanoparticles

The increasing demand for energy has triggered tremendous research efforts for the development of lightweight and durable energy storage devices. This requires exploring simple and economical methods to prepare the active materials and to design lightweight, flexible, free-standing supercapacitor electrodes in an inexpensive binder-free process. Herein, we try to address both these critical issues using CNOs and their composite with CuO as the active material. Active materials were supported on cotton wipes by a simple "sonication and drying" process to obtain light-weight, flexible and free-standing binder-free electrodes. In a symmetrical two-electrode cell, a pristine CNO electrode delivers a specific capacitance of 102.16 F g(-1) (20 mV s(-1)), an energy density of 14.18 W h kg(-1) and a power density of 2448 W kg(-1), which are the highest values reported so far for CNO-based materials. CNO-CuO nanocomposites demonstrate a very significant specific capacitance of 420 F g-1 (10 mV s(-1)) with deliverable energy and power density at 58.33 W h kg(-1) and 4228 W kg(-1), respectively. Electrodes of both the active materials show an excellent cyclic performance and stability, retaining up to 90-95% of their initial capacitance after 5000 charge-discharge cycles at a current density of 5 A g(-1). A simple cost estimation indicates that our device can deliver an energy density of 58.33 W h kg(-1) at an estimated cost of less than 1 $

In-situ synthesis and optical properties of CNO-ZnO nanocomposite

Carbon onions offer a good model system to study the optoelectronic properties of graphitic nano particles in zero dimension as they are favored over the planar graphite-like structures and energetically stable. Defect induced optical absorbance and luminescence behavior of as prepared CNOs has been investigated at room temperature considering their potential applications in optoelectronic devices. Most interestingly, these CNOs show exceptional excitation wavelength independent strong luminescence property over a range of the ultraviolet spectrum. By incorporating ZnO into CNO we observed sharp characteristic emissive peaks at 306 and 608 nm which arises due to the defect-mediated luminescence from localized metal oxide surface states by the photo-generated recombination of electron-hole pairs. The interaction between CNO and ZnO is through the functional groups on CNO which act as anchoring sites and nucleation points, leading to the bond formation between them. (C) 2016 Elsevier B.V. All rights reserved

Nanoporous gold-copper oxide based all-solid-state micro-supercapacitors

The rapid growth of miniaturized electronic devices has increased the demand for energy storage devices with small dimensions. Micro-supercapacitors have great potential to supplement or replace batteries and electrolytic capacitors for a wide range of applications. Micro-supercapacitor can be fabricated with microelectronic devices for efficient energy storage unit. However, the lower energy densities of micro-supercapacitors are still a bigger challenge to its application in micro devices. In this paper, we report all-solid-state nanoporous gold (NPG)-copper oxide (CuO) based micro-supercapacitor prepared using a simple fabrication process. In this process, first NPG interdigital patterns were developed by using a simple annealing and dealloying procedure, and then CuO was electrodeposited on NPG interdigital microelectrodes. The nanoporous gold substrate provides good electronic/ionic conductivity with high intrinsic surface area for the electrodeposition of CuO, which forms a novel hybrid electrode. The NPG-CuO micro-supercapacitor exhibits maximum areal capacitance 26 mF cm(-2), maximum specific energy 3.6 mu W h cm(-2) and maximum specific power 646 mW cm(-2). NPG-CuO micro-supercapacitors show excellent cyclic stability with 98% capacitance retention after 10 000 cycles